Energy harvesting can provide energy for electronic systems to make the electronic systems autonomous. The energy is obtained or harvested from renewable sources such as solar energy, wind energy, thermal energy, and kinetic energy. The energy provided by the energy source or sources can vary and may be interruptible. Electronic systems can include devices that require a regulated power source. Power converter circuits can be used to provide a regulated supply. Because of the desired autonomy of electronic systems, it can be important for the power converting process to be highly efficient and at the same time be robust in less than ideal conditions. The present inventors have recognized a need for improved performance of power converter circuits.